1. Field of the Invention
The present invention relates generally to a roller shifting device for a printing press. More specifically, the invention relates to a roller shifting device for shifting a plurality of rollers for contacting with and releasing away from the peripheral surface of an form dampening roller, in conjunction with shifting of the inking for contacting with and releasing away from the peripheral surface of a plate mounted on a plate cylinder.
2. Description of the Related Art
In general, an inking device and dampening device in a printing press are provided roller shifting devices for shifting rollers. For example, Japanese patent publication (Kohkohu) No. 2-36387, published on Aug. 16, 1990, discloses such type of the roller shifting device.
The construction of the roller shifting device as disclosed in the Japanese patent publication No. 2-36387 will be briefly discussed with reference to FIG. 11. The shown arrangement includes an form dampening roller 52 and a transfer roller 53. The form dampening roller is supported by a supporting member 56 pivotable about a pivot shaft 54 so that it is shifted to contact with and released away from a surface of a plate (not shown) mounted on a plate cylinder 51. Similarly, the transfer roller 53 is supported by a support member 57 pivotable about a pivot shaft 55 so that it is shifted to contact with and released away from the form dampening roller 52. In addition, the transfer roller 53 is held in contact with a dampening roller 64 which is stationarily positioned and partly disposed within a dampening reservoir 65. Therefore, the transfer roller 53 is shifted along the periphery of the water fountain roller 64.
The supporting members 56 and 57 are linked through a linkage lever 58. The linkage lever 58 is formed with an elongated slot 59 so as to permit displacement of the supporting member 56 relative to the other supporting member 57. An actuation rod 61 of an air cylinder 60 is connected to the supporting member 57.
In the operation for shifting the form dampening roller 52 away from the plate surface and shifting the transfer roller 53 away from the peripheral surface of the form dampening roller, the air cylinder 60 is actuated to retract the actuation rod 61. By this action of the actuation rod 61, the supporting member 57 is initially pulled to pivot in a direction shifting the transfer roller away from the form dampening roller 52. After a shifting stroke corresponding to the stroke of the elongated slot 59 of the linkage lever 58, the retraction force acts on the supporting member 56 to shift the form dampening roller 52 away from the plate surface. Therefore, the magnitude of angular displacement in the pivoting motion of the supporting member 56 becomes smaller than that of the supporting member 57 in the corresponding magnitude to the length of the elongated slot 59.
Upon contacting the form dampening and transfer rollers 52 and 53 onto respective of the mating surfaces, the air cylinder 60 is actuated in the opposite direction to extract the actuation rod 61. Then, the supporting member 57 is initially shifted for the pivoting stroke corresponding to the length of the elongated slot 59. At the end of the initial stroke of action of the actuation rod, the transfer roller carried by the supporting member 57 comes into contact with the form dampening roller 52. Then, according to the further stroke of extraction of the actuation rod 61, the supporting member 56 is pivoted together with the supporting member 57 so as to place the form dampening roller 52 in contact with the plate surface of the plate on the plate cylinder 51.
In such prior proposed construction of the roller shifting device, it is possible to shift the form dampening roller relative to the plate surface in conjunction with shifting of the transfer roller with respect to the form dampening roller. However, it does not shift other rollers contacting with the peripheral surface of the form dampening roller (for example, an intermediate roller 62 and a vibration roller 63). Therefore, these rollers are apt to be maintained in contact with the form dampening roller for a long period. This tends to cause the contact pressure to act on the outer periphery of the form dampening roller via these rollers, i.e. the intermediate roller, the vibration roller or so forth, while the form dampening roller is resting. It is also possible to provide a frictional force due to axial reciprocating motion of these rollers during resting of the form dampening roller to cause deformation in the form dampening roller and/or these rollers. Such deformation of the rollers may cause an uneven contour of the form dampening roller onto the plate surface to degrade quality of print.
To avoid degradation of printing quality, it becomes necessary to replace the form dampening roller or other rollers in a short period thus raising running cost.